Let me confirm what you're saying.
PM (windows?) loads up OK, but when you try to open an existing or create new publication, you get the error "'cannot paste from clipboard. Cannot read the available clipboard formats"?
!. PM6.5 can only be operated on a contemporary OS, like Win98SE or Win2K. Generally speaking, with later versions on Windows, it's a non-starter. If this is the case, and it's essential you open your PM files, download and install the trial version of PM7.
2. You probably have some corruption somewhere. You can try trashing all the configuration files (search using the string PM65*.cnf ) and re-loading PM65
3. If suggestion 2 fails, you need to remove and re-install PM65, but even this may not work. See 7.6 - Re-installing PageMaker of this linked PDF which was taken from the old AdobeForums FAQs. (Note the date of this FAQs and begin to realise how ancient PM65 is.)
4. Forget all the above, and move to InDesign.
Iechyd da! John
23:09 15/09/2009 BST